This invention relates to a specimen observation apparatus capable of obtaining both an optical microscope image and a scanning electron microscope image from one specimen simultaneously.
For observing biological specimens such as cells, it has been the recent practice to make comparison between an image obtained from an optical microscope (hereinafter referred to a "OM") and an image obtained from a scanning electron microscope (hereinafter referred to as "SEM"). An apparatus has been previously proposed for observing one region on one specimen at one time with both OM and SEM. Such apparatus includes a transparent glass plate having a transparent and electric conductive layer on a surface thereof for supporting a specimen in a vacuum column. The specimen is illuminated with light to create thereby an OM image with the light passing through the specimen. At the same time, the specimen is illuminated with electron beam to create thereby a SEM image based on information obtained by scanning the electron beam over the specimen. However, since at least the objective lens section of the OM is fixedly arranged adjacent to the glass plate with the vacuum column, the magnification of the OM image is not freely variable. The objective lens determines the magnification of the OM image. Nevertheless, it is necessary to provide a selection of magnifications to meet a variety of specimens. Changing the magnifications of the OM image would be a troublesome, time-consuming operation that involves breaking the vacuum in the vacuum column or specimen chamber and replacing the objective lens with another.
Accordingly, an object of this invention is to provide a specimen observation apparatus for enabling easy selection of the OM image magnification without breaking the vacuum within the column.